U.S. patent application number 17/414531 was filed with the patent office on 2022-02-24 for aligning optical circuit and aligning method.
The applicant listed for this patent is Nippon Telegraph and Telephone Corporation. Invention is credited to Hiroshi Fukuda, Yoshiho Maeda, Toru Miura.
Application Number | 20220057584 17/414531 |
Document ID | / |
Family ID | 1000005997434 |
Filed Date | 2022-02-24 |
United States Patent
Application |
20220057584 |
Kind Code |
A1 |
Miura; Toru ; et
al. |
February 24, 2022 |
ALIGNING OPTICAL CIRCUIT AND ALIGNING METHOD
Abstract
An alignment optical circuit includes: a plurality of grating
couplers that are formed on a substrate and arranged on a line; a
plurality of optical waveguides that are connected to the plurality
of grating couplers, respectively. Further, the alignment optical
circuit includes an optical sensor that is formed on the substrate
and measures optical intensity at a first light-receiving spot and
a second light-receiving spot on a line along an arrangement
direction of the plurality of grating couplers.
Inventors: |
Miura; Toru; (Tokyo, JP)
; Maeda; Yoshiho; (Tokyo, JP) ; Fukuda;
Hiroshi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nippon Telegraph and Telephone Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
1000005997434 |
Appl. No.: |
17/414531 |
Filed: |
December 3, 2019 |
PCT Filed: |
December 3, 2019 |
PCT NO: |
PCT/JP2019/047221 |
371 Date: |
June 16, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/4249 20130101;
G02B 6/26 20130101; G02B 6/4231 20130101; G02B 6/12 20130101; G02B
6/4292 20130101 |
International
Class: |
G02B 6/42 20060101
G02B006/42; G02B 6/12 20060101 G02B006/12; G02B 6/26 20060101
G02B006/26 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 17, 2018 |
JP |
2018-235211 |
Claims
1.-7. (canceled)
8. An alignment optical circuit comprising: a plurality of grating
couplers on a substrate and arranged on a line; a plurality of
optical waveguides connected to the plurality of grating couplers;
and an optical sensor on the substrate and configured to measure
optical intensity at two light-receiving spots on a line along an
arrangement direction of the plurality of grating couplers, wherein
an interval between the two light-receiving spots is an interval
between two of the plurality of grating couplers.
9. The alignment optical circuit according to claim 8, wherein: the
optical sensor includes a light-receiving region that extends along
the arrangement direction and corresponds to the two
light-receiving spots.
10. The alignment optical circuit according to claim 8, wherein the
optical sensor comprises a sensor at each of the two
light-receiving spots.
11. The alignment optical circuit according to claim 8, wherein the
interval between the two light-receiving spots is an interval
between respective ends of the plurality of grating couplers.
12. An alignment optical circuit comprising: a plurality of grating
couplers on a substrate and arranged on a line; a plurality of
optical waveguides connected to the plurality of grating couplers;
and a plurality of optical sensors on the substrate and arranged
along an arrangement direction of the plurality of grating
couplers.
13. The alignment optical circuit according to claim 12, wherein
the plurality of optical sensors is configured to measure optical
intensity at two light-receiving spots on a line along an
arrangement direction of the plurality of grating couplers, wherein
an interval between the two light-receiving spots is the same as an
interval between two of the plurality of grating couplers.
14. The alignment optical circuit according to claim 13, wherein
the plurality of optical sensors includes a light-receiving region
that extends along the arrangement direction and corresponds to the
two light-receiving spots.
15. The alignment optical circuit according to claim 13, wherein
the plurality of optical sensors comprises a sensor at each of the
two light-receiving spots.
16. An alignment method for aligning a first grating coupler and a
second grating coupler with a first optical fiber and a second
optical fiber, respectively, using an alignment optical circuit
including a plurality of grating couplers on a substrate and
arranged on a line, a plurality of optical waveguides connected to
the plurality of grating couplers, and an optical sensor on the
substrate and configured to measure optical intensity at two
light-receiving spots on a line along an arrangement direction of
the plurality of grating couplers, wherein the first grating
coupler and the second grating coupler are comprised by the
plurality of grating couplers, and the first optical fiber and the
second optical fiber are comprised by a fiber array comprising a
plurality of optical fibers arranged in a line, the alignment
method comprising: a first step of arranging the fiber array with a
light-emitting direction of each of the plurality of optical fibers
directed to a side of the alignment optical circuit; a second step
of causing the fiber array to move in a direction perpendicular to
the arrangement direction of the grating couplers and pass over the
optical sensor within a plane parallel to a plane of the alignment
optical circuit in a state in which light is emitted from the first
optical fiber and the second optical fiber to the side of the
alignment optical circuit and measuring an intensity change of each
of first light emitted from the first optical fiber and second
light emitted from the second optical fiber at the two
light-receiving spots; a third step of finding an angle formed by
the arrangement direction of the plurality of grating couplers and
an arrangement direction of the plurality of optical fibers within
the plane parallel to the plane of the alignment optical circuit
from a difference between the intensity change of the first light
and the intensity change of the second light that are measured by
the optical sensor; and a fourth step of rotating the arrangement
direction of the plurality of optical fibers by the angle found in
the third step within the plane parallel to the plane of the
alignment optical circuit to perform alignment.
17. The alignment method according to claim 16, wherein the optical
sensor includes a light-receiving region that extends along the
arrangement direction and corresponds to the two light-receiving
spots.
18. The alignment method according to claim 16, wherein the optical
sensor comprises a sensor at each of the two light-receiving spots.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a national phase entry of PCT
Application No. PCT/JP2019/047221, filed on Dec. 3, 2019, which
claims priority to Japanese Application No. 2018-235211, filed on
Dec. 17, 2018, which applications are hereby incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates to an alignment optical
circuit and an alignment method and, more specifically, to an
alignment optical circuit and an alignment method used for the
optical connection between a grating coupler and an optical
fiber.
BACKGROUND
[0003] For optically connecting a silicon optical circuit and an
optical fiber to each other (optical connection), a spot size
convertor, a spherical tip fiber, or the like has been used to
increase the efficiency of the optical connection between a
waveguide end surface and the optical fiber. In recent years, many
examples in which a silicon waveguide is provided with a grating
including grooves having a width of several hundred nanometers,
caused to function as a grating coupler that radiates light upward
and downward from an optical waveguide onto a substrate surface,
and optically connected to an optical fiber have been seen with the
development of microfabrication technologies.
[0004] For example, there has been proposed a technology in which a
grating coupler is used for optical connection with an optical
fiber in silicon photonics (see NPL 1). According to the
technology, the emission angle of light from the grating coupler to
the upper surface of the light becomes an angle satisfying Formula
(1) described in page 7870 of NPL 1 and is set to be an inclination
angle within 20 degrees from a direction perpendicular to a
substrate. The advantage of using the grating coupler is that the
light can be input to and output from the surface of the substrate
from above. For this reason, the technology of optical connection
using a grating coupler is suitable for the examination of each
optical circuit in a state in which a plurality of optical circuits
are formed on a wafer, or the like.
[0005] When light is coupled to a grating coupler, a single mode
fiber (SMF), a fiber array, or the like is used. For example, in an
optical circuit, an input grating coupler is provided at the light
input end of the optical circuit and an output grating coupler is
provided at the light output end of the optical circuit to be used
to examine the optical circuit. For example, light emitted from an
input SMF is optically connected to the input grating coupler. On
the other hand, light emitted from the output grating coupler is
optically connected to an output SMF to be extracted and used to
examine the optical circuit.
[0006] In this case, the alignment between the input SMF and the
input grating coupler and the alignment between the output SMF and
the output grating coupler are required. In order to perform the
alignment in a single alignment device, it is presumed as shown in
FIG. 13 that a fiber array 304 in which a plurality of SMFs are
bundled together is used, and that a plurality of grating couplers
301 connected to an optical waveguide 302 of an optical circuit 300
that is an object to be examined are arranged at the arrangement
pitch of the SMFs of the fiber array 304.
[0007] For example, when a SMF at one end of the fiber array 304
and a corresponding grating coupler 301 are used for input and a
SMF at the other end of the fiber array 304 and a corresponding
grating coupler 301 are used for output, alignment for both the
input and the output can be performed in a single optical alignment
system (device). Further, it is also possible to measure the state
of optical coupling in the plurality of grating couplers of the
optical circuit 300 using the respective grating couplers 301 with
the configuration described above.
CITATION LIST
Non Patent Literature
[0008] NPL 1 C. Li et al., "CMOS-compatible high efficiency
double-etched apodized waveguide grating coupler", Optics Express,
vol. 21, no. 7, pp. 7868-7874, 2013.
SUMMARY
Technical Problem
[0009] However, when the fiber array 304 is used as described
above, the alignment between the plurality of SMFs and the
plurality of grating couplers 301 is performed at the same time.
When the fiber array 304 is used, it is difficult to optically
connect the plurality of grating couplers 301 and the plurality of
SMFs to each other at the same time and in an optimum state if the
fiber array 304 is rotated (deviated) about a Z-axis that is the
normal line direction of the plane of the optical circuit 300 and
about an X-axis that is a direction perpendicular to the
arrangement direction of the plurality of SMFs of the fiber array
as shown in FIG. 14.
[0010] Embodiments of the present invention have been made in order
to solve the above problem and has an object of making it possible
to easily perform alignment for obtaining the optical connection
between a plurality of optical fibers of a fiber array in which the
plurality of optical fibers are bundled together and corresponding
grating couplers.
Means for Solving the Problem
[0011] An alignment optical circuit according to embodiments of the
present invention includes: a plurality of grating couplers that
are formed on a substrate and arranged on a line; a plurality of
optical waveguides that are connected to the plurality of grating
couplers, respectively; and an optical sensor that is formed on the
substrate and measures optical intensity at two light-receiving
spots on a line along an arrangement direction of the plurality of
grating couplers. An interval between the two light-receiving spots
is an interval between any two of the plurality of grating
couplers.
[0012] In a configuration example of the alignment optical circuit,
the optical sensor includes a light-receiving region that involves
the two light-receiving spots and extends along the arrangement
direction.
[0013] In a configuration example of the alignment optical circuit,
the optical sensor is formed at each of the two light-receiving
spots.
[0014] In a configuration example of the alignment optical circuit,
the interval between the two light-receiving spots is an interval
between both ends of the plurality of grating couplers.
[0015] An alignment optical circuit according to embodiments of the
present invention includes: a plurality of grating couplers that
are formed on a substrate and arranged on a line; a plurality of
optical waveguides that are connected to the plurality of grating
couplers, respectively; and a plurality of optical sensors that are
formed on the substrate and arranged along an arrangement direction
of the plurality of grating couplers.
[0016] An alignment method according to embodiments of the present
invention is an alignment method for aligning an alignment optical
circuit including a plurality of grating couplers that are formed
on a substrate and arranged on a line, a plurality of optical
waveguides that are connected to the plurality of grating couplers,
respectively, and an optical sensor that is formed on the substrate
and measures optical intensity at two light-receiving spots on a
line along an arrangement direction of the plurality of grating
couplers, and a first grating coupler and a second grating coupler
that are any two of the plurality of grating couplers and a first
optical fiber and a second optical fiber that are any two of
optical fibers of a fiber array in which the plurality of optical
fibers are arranged in a line, the alignment method including: a
first step of arranging the fiber array with a light-emitting
direction of each of the plurality of optical fibers directed to a
side of the alignment optical circuit; a second step of causing the
fiber array to move in a direction perpendicular to the arrangement
direction of the grating couplers and pass over the optical sensor
within a plane parallel to a plane of the alignment optical circuit
in a state in which light is emitted from the first optical fiber
and the second optical fiber to the side of the alignment optical
circuit and measuring an intensity change of each of first light
emitted from the first optical fiber and second light emitted from
the second optical fiber at the two light-receiving spots; a third
step of finding an angle formed by the arrangement direction of the
plurality of grating couplers and an arrangement direction of the
plurality of optical fibers within the plane parallel to the plane
of the alignment optical circuit from a difference between the
intensity change of the first light and the intensity change of the
second light that are measured by the optical sensor; and a fourth
step of rotating the arrangement direction of the plurality of
optical fibers by the angle found in the third step within the
plane parallel to the plane of the alignment optical circuit to
perform alignment.
[0017] An alignment method according to embodiments of the present
invention is an alignment method for aligning an alignment optical
circuit including a plurality of grating couplers that are formed
on a substrate and arranged on a line, a plurality of optical
waveguides that are connected to the plurality of grating couplers,
respectively, and a plurality of optical sensors that are arranged
along an arrangement direction of the plurality of grating
couplers, and a first grating coupler and a second grating coupler
that are any two of the plurality of grating couplers and a first
optical fiber and a second optical fiber that are any two of
optical fibers of a fiber array in which the plurality of optical
fibers are arranged in a line, the alignment method including: a
first step of arranging the fiber array in a state in which light
emitted from each of the plurality of optical fibers is received by
any of the plurality of optical sensors; a second step of causing
the fiber array to move in a direction distant from a plane of the
alignment optical circuit in a state in which the light is emitted
from the first optical fiber and the second optical fiber to a side
of the alignment optical circuit and measuring an intensity change
of each of first light emitted from the first optical fiber and
second light emitted from the second optical fiber by the plurality
of optical sensors; a third step of finding an angle formed by a
plane of the substrate and an arrangement direction of the
plurality of optical fibers about an axis perpendicular to the
arrangement direction of the plurality of grating couplers from a
difference between the intensity change of the first light and the
intensity change of the second light that are measured by the
plurality of optical sensors; and a fourth step of rotating the
arrangement direction of the plurality of optical fibers by the
angle found in the third step about the axis to perform
alignment.
Effects of Embodiments of the Invention
[0018] As described above, since a plurality of light-receiving
spots are provided on a substrate on which a plurality of grating
couplers are formed according to embodiments of the present
invention, it is possible to easily perform alignment for obtaining
the optical connection between a plurality of optical fibers of a
fiber array in which the plurality of optical fibers are bundled
together and corresponding grating couplers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1A is a plan view showing the configuration of an
alignment optical circuit according to a first embodiment of the
present invention.
[0020] FIG. 1B is a flowchart for describing an alignment method
according to the first embodiment of the present invention.
[0021] FIG. 2 is a diagram for describing a state in which the
arrangement direction of a plurality of optical fibers constituting
a fiber array is rotated by an angle .theta. about a Z-axis with
respect to a Y-axis.
[0022] FIG. 3 is a characteristic diagram showing the relationship
between a positional deviation amount .DELTA.x in an X-axis
direction between a first optical fiber 104a and a second optical
fiber 104j and the rotational angle .theta. between a state in
which the fiber array is not rotated about the Z-axis and a state
in which the fiber array is rotated by .theta. degrees about the
Z-axis.
[0023] FIG. 4 is a characteristic diagram showing an intensity
change (a) measured at a first light-receiving spot 131 and an
intensity change (b) measured at a second light-receiving spot 132
when the fiber array is moved.
[0024] FIG. 5 is a plan view showing a part of the configuration of
another alignment optical circuit according to the first embodiment
of the present invention.
[0025] FIG. 6A is a plan view showing the configuration of an
alignment optical circuit according to a second embodiment of the
present invention.
[0026] FIG. 6B is a flowchart for describing an alignment method
according to the second embodiment of the present invention.
[0027] FIG. 7 is a diagram for describing a state in which the
arrangement direction of a plurality of optical fibers constituting
a fiber array is rotated by an angle .theta.2 about an X-axis with
respect to a Y-axis.
[0028] FIG. 8 is a characteristic diagram showing the changes of
deviation amounts .DELTA.Y_a and .DELTA.Y_j as .theta.2 changes
when a distance H is 100 .mu.m.
[0029] FIG. 9 is a diagram for describing a state in which the
arrangement direction of the plurality of optical fibers
constituting the fiber array is rotated by the angle .theta.2 about
the X-axis with respect to the Y-axis.
[0030] FIG. 10 is a diagram for describing the measurement of
.DELTA.Y2 using a plurality of optical sensors 203a to 203h.
[0031] FIG. 11 is a characteristic diagram showing a light
intensity profile H at a distance H and a light intensity profile
H2 at a distance H2.
[0032] FIG. 12 is a characteristic diagram showing the relationship
between .theta.2 and .DELTA.Y2 when H2-H is equal to 100 .mu.m.
[0033] FIG. 13 is a perspective view for describing the state of
the alignment between a fiber array 304 in which a plurality of
SMFs are bundled together and a plurality of grating couplers
301.
[0034] FIG. 14 is a perspective view for describing the state of
the alignment between the fiber array 304 in which the plurality of
SMFs are bundled together and the plurality of grating couplers
301.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0035] Hereinafter, alignment optical circuits and alignment
methods according to embodiments of the present invention will be
described.
First Embodiment
[0036] To begin with, an alignment optical circuit according to a
first embodiment of the present invention will be described with
reference to FIG. 1A. First, the alignment optical circuit includes
a plurality of grating couplers 101a, 101b, 101c, 101d, 101e, 101f,
101g, 101h, 101i, and 101j that are formed on a substrate 100 and
arranged on a line and a plurality of optical waveguides 102a,
102b, 102c, 102d, 102e, 102f, 102g, 102i, 102h, and 102j that are
connected to the plurality of grating couplers 101a to 101j,
respectively. The plurality of grating couplers 101a to 101j are
arranged at even intervals on the same line (a line parallel to a
Y-axis). Further, the optical waveguides 102a to 102j are optically
connected to an optical circuit that is formed on the substrate 100
and not shown. Note that a direction in which the plurality of
grating couplers 101a to 101j are arranged is a Y-axis
direction.
[0037] Further, the alignment optical circuit includes an optical
sensor 103 that is formed on the substrate 100 and measures optical
intensity at a first light-receiving spot 131 and a second
light-receiving spot 132 on a line along the arrangement direction
(Y-axis direction) of the plurality of grating couplers 101a to
101j. In the first embodiment, the optical sensor 103 includes a
light-receiving region that involves the first light-receiving spot
131 and the second light-receiving spot 132 and extends along the
arrangement direction (Y-axis direction) of the plurality of
grating couplers 101a to 101j.
[0038] The alignment optical circuit performs alignment in relation
to a rotational deviation about a Z-axis between the arrangement
direction of a plurality of optical fibers constituting a fiber
array that is an object to be aligned and the arrangement direction
(Y-axis direction) of the plurality of grating couplers 101a to
101j. That is, a rotational deviation angle about the Z-axis
between the arrangement direction of the plurality of optical
fibers constituting the fiber array that is an object to be aligned
and the arrangement direction (Y-axis direction) of the plurality
of grating couplers 101a to 101j is found by the alignment optical
circuit. Note that the Z-axis is an axis perpendicular to the plane
of the substrate 100.
[0039] The interval between the first light-receiving spot 131 and
the second light-receiving spot 132 at which the optical sensor 103
performs optical intensity measurement is the interval between any
two of the plurality of grating couplers 101a to 101j. The interval
between the first light-receiving spot 131 and the second
light-receiving spot 132 is, for example, the interval between both
ends of the plurality of grating couplers 101a to 101j. Note that
an object to be aligned using the alignment optical circuit is the
fiber array in which the plurality of optical fibers are arranged
in a line. The fiber array is, for example, a fiber array in which
ten optical fibers are arranged in a line.
[0040] The optical sensor 103 can be constituted by, for example, a
well-known surface incident photo diode (PD). As such, a GePD
including a light absorption layer made of germanium, a SiPD
including a light absorption layer made of silicon, or the like can
be used. The optical sensor 103 is required to have, as a length in
the Y-axis direction of the light-receiving region, a length at
which light emitted from each of a first optical fiber 104a and a
second optical fiber 104j that serve as objects to be aligned in
the fiber array can be received. For example, when the fiber array
is constituted by ten optical fibers and the interval between the
adjacent optical fibers is 127 .mu.m, the interval between the
first optical fiber 104a and the second optical fiber 104j at both
ends of the fiber array is 1143 .mu.m. In this case, the length in
the Y-axis direction of the light-receiving region of the optical
sensor 103 is set to be longer than 1143 .mu.m.
[0041] Next, an alignment method according to the first embodiment
will be described using the flowchart of FIG. 1B. First, in a first
step S101, the fiber array is arranged with the light-emitting
direction of each of the plurality of optical fibers of the fiber
array directed to the side of the alignment optical circuit. Note
that the fiber array is rotated by a prescribed angle about the
Y-axis that is a direction in which the plurality of optical fibers
are arranged. The angle is the incident and emitting angle of light
determined by the structure of the grating couplers, and set to be,
for example, an inclination angle within 20 degrees from a
direction perpendicular to the substrate plane of the alignment
optical circuit in NPL 1.
[0042] Next, in a second step S102, in a state in which light is
emitted from the first optical fiber 104a and the second optical
fiber 104j to the side of the alignment optical circuit, the fiber
array is caused to move in a direction (X-axis direction)
perpendicular to the arrangement direction of the grating couplers
101a to 101j and pass over (move on) the optical sensor 103 within
a plane parallel to the plane of the alignment optical circuit.
[0043] For example, with the alignment optical circuit (or the
fiber array) fixed onto an electric stage having a stepping motor
or the like, the electric stage is caused to move. That is, the
passage of the fiber array described above can be performed in such
a manner that the alignment optical circuit is caused to relatively
move with respect to the fiber array. Thus, the intensity change of
each of first light emitted from the first optical fiber 104a and
second light emitted from the second optical fiber 104j is measured
at each of the first light-receiving spot 131 and the second
light-receiving spot 132 of the optical sensor 103 (intensity
change measurement). For example, each of photocurrents flowing
through the first light-receiving spot 131 and the second
light-receiving spot 132 of the optical sensor 103 is measured at
the same time. When a deviation amount in the .theta.z direction of
the fiber array is small, the two light is incident on the PD at
the same time. Therefore, there is a possibility that the
photocurrents generated by the two light cannot be separated from
each other. In this case, the two light is not measured at the same
time, but the measurement is performed with light emitted from one
fiber and then performed with light emitted from the other fiber.
In this manner, the photocurrents can be separated and
measured.
[0044] Next, in a third step S103, an angle .theta. formed by the
arrangement direction (Y-axis direction) of the plurality of
grating couplers 101a to 101j and the arrangement direction of the
plurality of optical fibers in the fiber array within the plane
parallel to the substrate plane of the alignment optical circuit is
found from the difference between the intensity change of the first
light and the intensity change of the second light that are
measured by the optical sensor 103 (angle calculation).
[0045] For example, in a state in which the arrangement direction
of the plurality of optical fibers constituting the fiber array is
rotated by the angle .theta. about a Z-axis with respect to the
direction (Y-axis) in which the plurality of grating couplers 101a
to 101j are arranged as shown in FIG. 2, it is difficult to align
each of all the optical fibers and the grating couplers 101a to
101j at the same time. For example, even if alignment is performed
so that the optical connection between an optical fiber near the
center of the fiber array and a corresponding grating coupler
becomes optimum, the optical connection between optical fibers
distant from the center of the fiber array and corresponding
grating couplers causes large coupling loss. In a state in which
the large coupling loss is caused, the port dependency of the
insertion loss of an optical signal with respect to the optical
circuit is also caused.
[0046] For example, in a case in which the fiber array is
constituted by ten optical fibers, the positional relationship
between the first optical fiber 104a and the second optical fiber
104j at both ends of the fiber array when the fiber array is
rotated by .theta. degrees about the Z-axis with its center as a
rotational center creates a state shown in FIG. 2. When the
interval between the adjacent optical fibers of the fiber array is
127 .mu.m, a distance D between the first optical fiber 104a and
the second optical fiber 104j becomes 1143 .mu.m.
[0047] In this case, the relationship between a positional
deviation amount .DELTA.x in the X-axis direction between the first
optical fiber 104a and the second optical fiber 104j and the
rotational angle .theta. between a state in which the fiber array
is not rotated about the Z-axis and a state in which the fiber
array is rotated by .theta. degrees about the Z-axis is shown in
FIG. 3. When .theta. is zero, the positional deviation amount
.DELTA.x in the X-axis direction between the first optical fiber
104a and the second optical fiber 104j becomes zero. On the other
hand, for example, when .theta. becomes only 0.5 degrees, it is
found that .DELTA.X becomes about 10 .mu.m, and that the positional
deviation of each of the first optical fiber 104a and the second
optical fiber 104j from a corresponding grating coupler becomes 5
.mu.m. When consideration is given to the fact that the optical
fibers have a core diameter of about 10 .mu.m, the numerical value
described above results in a crucial positional deviation.
[0048] The positional deviation by rotation about the Z-axis of the
fiber array is found in the first step S101 to the third step S103
described above. In the intensity change measurement of the second
step S102, intensity changes (a) and (b) are measured at the first
light-receiving spot 131 and the second light-receiving spot 132,
respectively, as shown in FIG. 4 when the fiber array is moved.
From the difference between the intensity changes (a) and (b), the
angle .theta. is found. For example, the deviation between the peak
position of the intensity change (a) and the peak position of the
intensity change (b) corresponds to .DELTA.X. In an example shown
in FIG. 4, .DELTA.X is equal to 6 .mu.m. When .DELTA.X is equal to
6 .mu.m, it is found from the relationship between .DELTA.X and
.theta. described above using FIGS. 2 and 3 that .theta. is equal
to 0.3 degrees.
[0049] After the angle .theta. formed by the arrangement direction
(Y-axis direction) of the plurality of grating couplers 101a to
101j and the arrangement direction of the plurality of optical
fibers of the fiber array is found as described above, the
arrangement direction of the plurality of optical fibers of the
fiber array is rotated by the angle found in the third step within
the plane parallel to the substrate plane of the alignment optical
circuit to perform alignment in a fourth step S104 (rotation).
Further, the fiber array that has been subjected to the alignment
by the adjustment of the angle about the Z-axis is caused to move
parallel on the plane of the substrate 100 in a state in which the
adjusted angle is maintained, and arranged at the position of
optical connection with the plurality of grating couplers 101a to
101j.
[0050] Meanwhile, the one optical sensor 103 including the
light-receiving region that involves the first light-receiving spot
131 and the second light-receiving spot 132 and extends in the
Y-axis direction is used in the above description. However, a first
optical sensor 103a and a second optical sensor 103b that are
formed on the substrate 100 may be used as shown in FIG. 5. The
first optical sensor 103a and the second optical sensor 103b are
formed at the first light-receiving spot 131 and the second
light-receiving spot 132, respectively. The optical sensor 103 is
(the first optical sensor 103a and the second optical sensor 103b
are) only required to be arranged at any place on the substrate
100.
[0051] Further, in the above description, the angle formed by the
arrangement direction (Y-axis direction) of the plurality of
grating couplers and the arrangement direction of the plurality of
optical fibers within the plane parallel to the plane of the
alignment optical circuit is found from the difference between the
peak positions as the difference of the intensity change between
the first light emitted from the first optical fiber and the second
light emitted from the second optical fiber. However, the angle may
be found in a different way. For example, as the difference of the
intensity change between the first light emitted from the first
optical fiber and the second light emitted from the second optical
fiber, the angle formed by the arrangement direction (Y-axis
direction) of the plurality of grating couplers and the arrangement
direction of the plurality of optical fibers within the plane
parallel to the plane of the alignment optical circuit can be found
from the difference (deviation amount) between positions at which
the intensity of the first light and the intensity of the second
light become the same.
[0052] For example, there is a case that the peak position of one
intensity change does not appear in a range in which the fiber
array is caused to move in the X-axis direction since the width
(the length in the X-axis direction) of the optical sensor 103 is
large. In such a case, the above angle is found from the difference
between the spots of slopes that change in the same state
(positions at which the intensity becomes the same).
[0053] Note that in order to use the peak positions as the
difference of the intensity change between the first light emitted
from the first optical fiber and the second light emitted from the
second optical fiber, the width of the optical sensor 103 desirably
falls within a prescribed size considering an angle that is
required to be detected and the spot size of the light emitted from
the optical fibers as will be described below.
[0054] For example, when the fiber array is constituted by ten
optical fibers, the interval between the adjacent optical fibers is
127 .mu.m, and the spot size of light is 20 .mu.m, the width of the
optical sensor 103 is desirably 30 .mu.m or less to detect the
deviation of an angle .theta. of 0.5 degrees. Note that the
limitation value of the minimum width of the optical sensor 103 is
determined under the manufacturing constraints of the optical
sensor 103.
[0055] As described above, an optical sensor that measures light
intensity at two spots on a line extending along an arrangement
direction is provided on a substrate on which a plurality of
grating couplers are formed according to the first embodiment.
Therefore, alignment for obtaining the optical connection between a
plurality of optical fibers of a fiber array in which the plurality
of optical fibers are bundled together and corresponding grating
couplers can be easily performed.
Second Embodiment
[0056] Next, an alignment optical circuit according to a second
embodiment of the present invention will be described with
reference to FIG. 6A. The alignment optical circuit includes a
plurality of grating couplers 101a to 101j that are formed on a
substrate 100a and arranged on a line and a plurality of optical
waveguides 102a to 102j that are connected to the plurality of
grating couplers 101a to 101j, respectively. These elements are the
same as those of the first embodiment described above.
[0057] Further, the alignment optical circuit includes a plurality
of optical sensors 203a, 203b, 203c, 203d, 203e, 203f, 203g, and
203h that are formed on the substrate 100a and arranged along the
arrangement direction (Y-axis direction) of the plurality of
grating couplers 101a to 101j. Each of the optical sensors 203a to
203h includes a light-receiving region that extends in a direction
(X-axis direction) orthogonal to the arrangement direction of the
plurality of grating couplers 101a to 101j. The arrangement spot of
each of the optical sensors 203a to 203h serves as a
light-receiving spot. The alignment optical circuit performs
alignment in relation to a rotational deviation about an X-axis in
the arrangement direction of a plurality of optical fibers
constituting a fiber array that is an object to be aligned. That
is, a rotational deviation angle about the X-axis between the
arrangement direction of the plurality of optical fibers
constituting the fiber array that is an object to be aligned and
the plane of the substrate 100a is found by the alignment optical
circuit.
[0058] An object to be aligned using the alignment optical circuit
of the second embodiment is the fiber array in which the plurality
of optical fibers are arranged in a line. The fiber array is, for
example, a fiber array in which ten optical fibers are arranged in
a line.
[0059] Each of the optical sensors 203a to 203h can be constituted
by, for example, a well-known surface incident PD. As such, a GePD
including a light absorption layer made of germanium, a SiPD
including a light absorption layer made of silicon, or the like can
be used.
[0060] Each of the optical sensors 203a to 203h is required to
have, as a length in the X-axis direction of the light-receiving
region, a length at which light emitted from each of a first
optical fiber 104a and a second optical fiber 104j that serve as
objects to be aligned in the fiber array can be received.
[0061] The fiber array that is an object to be aligned is arranged
to be rotated about a Y-axis by a prescribed angle determined by
grating design from a direction perpendicular to the substrate
plane of the alignment optical circuit as described above in
optical connection with the plurality of grating couplers 101a to
101j. The angle described above is set to be, for example, within
20 degrees in NPL 1. When the rotation angle about the Y-axis is
.theta.Y, the length in the X-axis direction of the light-receiving
region described above is required to have a length considering
.theta.Y and the shift amounts in the X-axis direction of the
optical axes of the optical fibers and the spot size of light that
are determined from the relationship of the rising amount of the
fiber array that will be described later. The point will be
described later.
[0062] Next, an alignment method according to the second embodiment
will be described using the flowchart of FIG. 6B. First, in a first
step S111, the fiber array is arranged with the light-emitting
direction of each of the plurality of optical fibers of the fiber
array directed to the side of the alignment optical circuit. Note
that in the same manner as the above, the fiber array is rotated by
a prescribed angle about the Y-axis that is a direction in which
the plurality of optical fibers are arranged.
[0063] Next, in a second step S112, in a state in which light is
emitted from the first optical fiber 104a and the second optical
fiber 104j to the side of the alignment optical circuit, the fiber
array is caused to move in a direction distant from the plane of
the alignment optical circuit. For example, with the alignment
optical circuit (or the fiber array) fixed onto an electric stage
having a stepping motor or the like, the electric stage is caused
to move (vertically move). That is, the movement of the fiber array
described above can performed in such a manner that the alignment
optical circuit is caused to relatively move with respect to the
fiber array.
[0064] Each of first light emitted from the first optical fiber
104a and second light emitted from the second optical fiber 104j is
caused to pass over the plurality of optical sensors 203a to 203h
by the movement, and the intensity change of each of the first
light and the second light is measured by the plurality of optical
sensors 203a to 203h.
[0065] Next, in a third step S113, an angle .theta.2 formed by the
plane of the substrate 100 and the arrangement direction of the
plurality of optical fibers of the fiber array about the axis
(X-axis) perpendicular to the arrangement direction (Y-axis) of the
plurality of grating couplers 101a to 101j is found from the
difference between the intensity change of the first light and the
intensity change of the second light that are measured by the
plurality of optical sensors 203a to 203h (angle calculation).
[0066] For example, in a state in which the arrangement direction
of a plurality of optical fibers constituting a fiber array 104 is
rotated by the angle .theta.2 about the X-axis with respect to the
substrate plane as shown in FIG. 7, it is difficult to align each
of all the optical fibers and the grating couplers 101a to 101j at
the same time.
[0067] Here, a case in which the arrangement direction of the
plurality of optical fibers of the fiber array 104 is not parallel
to the substrate plane but is rotated about the X-axis is compared
with a case in which the arrangement direction is not rotated but
both the arrangement direction and the substrate plane are parallel
to each other (.theta.2=0 degree). First, an irradiation position
on the substrate of the light emitted from the first optical fiber
104a is deviated by .DELTA.Y_a between the case in which the
arrangement direction is rotated and the case in which the
arrangement direction is not rotated. Further, an irradiation
position on the substrate of the light emitted from the second
optical fiber 104j is deviated by .DELTA.Y_j between the case in
which the arrangement direction is rotated and the case in which
the arrangement direction is not rotated. Note that these deviation
amounts are produced when the fiber array 104 and the substrate
plane of the alignment optical circuit are separated from each
other by a distance H.
[0068] When the distance H described above is 100 .mu.m, the
deviation amounts .DELTA.Y_a and .DELTA.Y_j described above change
as shown in FIG. 8 as .theta.2 changes. Note that the results of
FIG. 8 are obtained from calculation. The deviation amounts
.DELTA.Y_a and .DELTA.Y_j increase as .theta.2 increases. Further,
the difference between the deviation amounts .DELTA.Y_a and
.DELTA.Y_j increases as .theta.2 increases.
[0069] Even if .theta.2 is constant, the deviation amounts
.DELTA.Y_a and .DELTA.Y_j described above also change as the
distance between the fiber array 104 and the substrate plane of the
alignment optical circuit changes. When the distance H between the
fiber array 104 and the substrate plane of the alignment optical
circuit is changed to a distance H2 as shown in FIG. 9, the
deviation amount of the irradiation position on the substrate of
the light emitted from the first optical fiber 104a increments by
.DELTA.Y2 from .DELTA.Y_a. Further, when the distance H between the
fiber array 104 and the substrate plane of the alignment optical
circuit is changed to the distance H2, the deviation amount of the
irradiation position on the substrate of the light emitted from the
second optical fiber 104j increments by .DELTA.Y2 from .DELTA.Y_j.
The changes of both the deviation amounts caused when the distance
H is changed to the distance H2 are .DELTA.Y2.
[0070] .DELTA.Y2 caused when the fiber array 104 is caused to move
in a direction distant from the plane of the alignment optical
circuit is found in the first step S111 to the third step S113
described above. As shown in FIG. 10, .DELTA.Y2 is measured using
the plurality of optical sensors 203a to 203h of which the planar
shape in each light-receiving region is a stripe shape extending in
the X-axis direction.
[0071] The plurality of optical sensors 203a to 203h has, as the
length in the X-axis direction of each light-receiving region, a
length considering .theta.Y and the shift amounts in the X-axis
direction of the optical axes of the optical fibers and the spot
size of light that are determined from the relationship of the
rising amount (H2-H) of the fiber array. Further, the arrangement
interval between the plurality of optical sensors 203a to 203h can
be determined by .theta.2 that is required to be found and a rising
amount from the distance H to the distance H2. Further, the length
in the Y-axis direction of each of the light-receiving regions of
the plurality of optical sensors 203a to 203h is required to be the
arrangement interval described above or less.
[0072] Light intensity profiles obtained by measuring the light
intensity of the light from the first optical fiber 104a and the
light from the second optical fiber 104j, which are irradiated onto
the optical sensors 203a to 203h in which the respective conditions
are set as described above, at each of the optical sensors 203a to
203h are compared with each other between a case before the fiber
array is caused to move and a case after the fiber array is caused
to move to calculate .DELTA.Y2.
[0073] For example, as shown in FIG. 11, a case in which a light
intensity profile H is obtained when the distance between the fiber
array and the substrate plane of the alignment optical circuit is H
and a case in which a light intensity profile H2 is obtained when
the distance between the fiber array and the substrate plane of the
alignment optical circuit is H2 are taken into consideration. In
the intensity profiles, a horizontal axis shows the optical sensors
203a to 203h, and the shift amount .DELTA.Y between the intensity
profile H and the intensity profile H2 is the interval between two
adjacent optical sensors. For example, when the arrangement
interval between the optical sensors 203a to 203h is 2 .mu.m,
.DELTA.Y is equal to 2 .mu.m. Further, the relationship between
.theta.2 and .DELTA.Y2 obtained when H2-H is equal to 100 .mu.m is
shown in FIG. 12. In this case, .theta.2 becomes approximately 1
degree when .DELTA.Y is equal to 2 m.
[0074] After the angle .theta.2 formed by the plane of the
substrate 100 and the arrangement direction of the plurality of
optical fibers in the fiber array about the X-axis is found as
described above, the arrangement direction of the plurality of
optical fibers of the fiber array is rotated by the angle found in
the third step within the plane parallel to the substrate plane of
the alignment optical circuit to perform alignment in a fourth step
S114 (rotation). Further, the fiber array that has been subjected
to the alignment by the adjustment of the angle about the X-axis is
caused to move parallel on the plane of the substrate 100 in a
state in which the adjusted angle is maintained, and arranged at
the position of optical connection with the plurality of grating
couplers 101a to 101j.
[0075] Meanwhile, the second embodiment describes a case in which
the eight optical sensors 203a to 203h are used as an example, but
two or more optical sensors are only required to be used. Further,
there is an advantage that the use of more optical sensors makes it
possible to find .DELTA.Y2 even in a case in which .DELTA.Y2 is
greater than the arrangement interval between the optical
sensors.
[0076] As described above, a plurality of optical sensors that are
arranged along the arrangement direction of a plurality of grating
couplers are provided on a substrate on which the plurality of
grating couplers are formed according to the second embodiment.
Therefore, alignment for obtaining the optical connection between a
plurality of optical fibers of a fiber array in which the plurality
of optical fibers are bundled together and corresponding grating
couplers can be easily performed.
[0077] As described above, a plurality of light-receiving spots are
provided on a substrate on which a plurality of grating couplers
are formed according to embodiments of the present invention.
Therefore, alignment for obtaining the optical connection between a
plurality of optical fibers of a fiber array in which the plurality
of optical fibers are bundled together and corresponding grating
couplers can be easily performed.
[0078] Note that it becomes obvious that the present invention is
not limited to the embodiments described above and many
modifications and combinations could be performed by persons with
ordinary knowledge in the field concerned within the technical
spirit of the present invention.
REFERENCE SIGNS LIST
[0079] 100 Substrate [0080] 100a Substrate [0081] 101a to 101j
Grating coupler [0082] 102a to 102j Optical waveguide [0083] 103
Optical sensor [0084] 103a First optical sensor [0085] 103b Second
optical sensor [0086] 104 Fiber array [0087] 104a First optical
fiber [0088] 104j Second optical fiber [0089] 131 First
light-receiving spot [0090] 132 Second light-receiving spot [0091]
203a to 203h Optical sensor.
* * * * *